Nitrates of lead are four :— Scxbaale nitrate of lead . . . aPbO, NO,+ Aq Trinitrate 2(3Pb0 NO,)+ SAq Dinitrate . . . . . 2Pb0, NO, +Aq Mononitrate . . . . Pb0, NO The last, or ordinary nitrate of lead is the only one of importance. It is readily made by dissolving oxide of lead in diluted nitric acid. On evaporating the solution it crystallises out in more or less opaque octahedra. It is soluble in eight times its weight of cold water; paper or tinder saturated with the solution and dried is thereby rendered exceedingly inflammable.
Hyponitrates and nitrites of lead are formed when metallic lead is boiled with nitrate of lead. The strength of the solution and the extent of ebullition determines which of these is produced. They are all more or less crystalline.
Borates of lead, result when boracic acid is fused with oxide of lead. One of them enters into the composition of Faraday's optical glass.
Silicate of lead is abundantly formed in the manufacture of flint glass. [GLASS.] Tungstate of lead occurs native. [LEAD, in NAT. HIST. Div.] It forms when ground up with oil a pigment resembling white lead.
Chronsates of lead.—The two principal are (1) neutral chromate, and (2) dichromate 1. Chromate of lead, or chrome yellow, occurs under many different names. [CoLounrna MATTERS.] It is obtained on adding a clear solution of neutral chromate of potash, soda, or lime, to a solution of nitrate or acetate of lead, well washing the precipitate and drying it out of any possible contact of sulphuretted hydrogen.
2. Dichromate of lead, or Orange chrome.—It is made by boiling white lead in a solution of bichromate of potash, or by fusing yellow chrome with five times its weight of nitre, and well washing the product.
For a description of the details necessary to be attended to for the production of lead chromes of various shades, see a paper in the Phar maceutical Journal,' vol. xv., pp. 66 and 69.
Tartrate of lead acetate of lead dis solved in water with half its weight of tartaric acid, and wash and dry the precipitate.
When tartrate of lead is heated in a closed tube it is decomposed, white vapours are evolved, and a mixture of metallic lead and carbon remain in an exceedingly minute state of division. On being thrown out into the air the mixture takes fire spontaneously, and is commonly known as the lead pyrophorous.
Acetates of lead. [ACETATE.] Alloys of lead. [Barrtor.m METAL; PEWTER ; SOLDERS ; SHOT ; TYPE-METAL.] Teats for lead.—This metal is recognised in solution by the yellow precipitate of chromate with chromate of potash ; white, soluble in excess with the alkalies; white, insoluble with sulphuric acid or a sulphate. The formation of iodide of lead by adding a few drops of iodide of potassium solution, is perhaps the moat characteristic test for lead, as the precipitate dissolves when heated, and is deposited again on cooling in the well-known beautiful golden yellow scales. Sulphuretted hydrogen is, however, the most delicate test for lead. The formation of arborescent crystals of lead, by suspending a piece of zinc in a solution of acetate of lead, is an illustration of how one metal, having more powerful affinities than another, becomes a test for the latter. Thus zinc is a test for lead.
Estimation of lead.—This is generally effected in the state of sulphate, which contains 68'31 per cent. of metal.